Individual landlords can be moral, upstanding people, and the incentive structure around deriving your income from rents can systemically produce inhumane outcomes. They are not mutually exclusive.
> It's also the only thing that produces new construction
It's not, though. People constructed housing for thousands of years without landlords. There are plenty of ways to fund constructions without markets. We have built a society that prefers to organize it that way, but that is also a society with more vacant units than there are homeless, where it is _normal_ to spend 50% or more of one's income on rent. Those outcomes, I argue, are inhumane, but also, maybe more controversially, avoidable in a system organized around something other than profit.
> On the other hand, as more speculators participate in a market, underlying real demand and supply can diminish compared to trading volume, and prices may become distorted.[8]
Note that I said "properly regulated and harnessed". The creation of bubbles is a temptation for both speculators and governments.
Specifically, derivatives and futures based on real estate should be treated by governments as toxic / illegal speculation. In fact, banning bad money from bubble-making practices amplifies the incentive for small landlords to improve and build living space on property.
I'm just starting being a landlord and I am one bad tenant away from copying the inhumane practices associated with companies that deal with a plethora of bad tenants. I purchase my home last year and I am renting below cost.
If everyone behaves nicely, it works out well for everyone. But if a party doesn't follow the agreement, everyone is in for a world of hurt.
It's also the only thing that produces new construction. Properly regulated and harnessed, the incentives are necessary to draw capital to building.